Neurons & the Action Potential

STRUCTURE - dendrites on motor neurons receive impulses and conduct them toward the cell body, then down the axon

Resting Potential In a resting neuron, there is a difference in electrical charges on the outside and inside of the plasma membrane. The outside has a positive charge and the inside has a negative charge

ATP energy, actively transports 3 Na+ out & 2 K+ ions into the cell, by the sodium-potassium pump.

How can the membrane be charged (positive on the outside and negative on the inside) when both Na and K are positive ions? ANS: Note that for every 3 Na+ ions moved, only 2 K+ ions move. Because more Na+ ions are moved out the outside is positive.

a resting membrane is POLARISED - the resting potential of the cell is approx. -70mV

Action Potential -when the cell mb is stimulated, there is a change in the permeability of the mb to Na+ ions - the mb becomes more permeable to Na+ and K+ --> Na+ ions diffuse into the cell disturbing the resting potential - the inside of the cell becomes more positive relative to the outside. (peak value = +30mV)

DEPOLARIZATION As the outside of the cell becomes more negative than the inside of the cell, the mb is now DEPOLARIZED. When enough sodium ions enter the cell to depolarize the mb to a critical level (threshold level) an action potential arises which generates an impulse. = all or none principle

REPOLARIZATION K+ leaves the cell charges switch the outside of the cell becomes more positive than the inside of the cell the mb is now repolarized

Refractory Period - after firing, the mb cannot send another signal for a short time = refractory period - until the mb stabilizes the action potential is higher than normal…

In multiple sclerosis, the myeline sheaths are attacked by the person’s own immune system resulting in scar tissue build up on the myelin. Symptoms of multiple sclerosis include: numbness, muscular weakness, lack of coordination, ultimately paralysis. Consider what you know about the importance of myelin explain the symptoms. ANS: Myelin is needed for proper nerve transmission. When it is damaged, transmission is too slow for normal function.

How do signals pass between neurons? Synapse = space between neurons chemical neurotransmitters are used to transmit signal

Classwork/ Homework Read 11.2 Supplement your notes as needed Complete #1, 2, 5